We derive an effective Hamiltonian for highly correlated $t_{2g}$ states centered at the Co sites of Na$_x$CoO$_2$. The essential ingredients of the model are an O mediated hopping, a trigonal crystal-field splitting, and on-site effective interactions derived from the exact solution of a multi-orbital model in a CoO$_6$ cluster, with parameters determined previously. The effective model is solved by dynamical mean-field theory (DMFT). We obtain a Fermi surface (FS) and electronic dispersion that agrees well with angle-resolved photoemission spectra (ARPES). Our results also elucidate the origin of the "sinking-pockets" in different doping regimes.
Asymmetric band widening by screened exchange competing with local correlations in SrVO3: new surprises on an old compound from combined GW and dynamical mean field theory GW+DMFT
最近，在真实材料中首次实现了组合GW和动态平均场方案“GW+DMFT”的动态实现[J. M. Tomczak等人，欧罗巴Lett. 100 67001（2012）]，并应用于三元过渡金属氧化物SrVO3。在这里，我们回顾并扩展了这项工作，不仅详细介绍了完整的GW+DMFT计算，而且还讨论和测试了简化的近似方案。我们深入了解交换和相关效应的性质：在费米液体制度SrVO3的动力学重整基本上是本地的，和非本地的相关性主要作用于筛选Fock交换项。后者实质上加宽了准粒子能带结构，而由前者引起的能带变窄伴随着向更高能量的光谱权重转移。最有趣的是，交换加宽在光谱的未被占据的部分中更加明显。其结果是，GW+DMFT电子结构的SrVO3类似于传统的密度泛函为基础的动态平均场（DFT+DMFT）的占有状态的描述，但深刻的修改，在空的部分。我们的工作导致逆光电子能谱（IPES）数据的重新解释。事实上，我们分配一个突出的峰在约2.7 eV的主要是EG状态，而不是一个上哈伯德带的t2g字符。对于其他过渡金属氧化物也可以预期类似的惊喜，这需要对导带态进行更详细的研究。
We present a dynamical mean-field study of two-particle dynamical response functions in two-band Hubbard model across several phase transitions. We observe that the transition between theexcitonic condensate and spin-state ordered state is continuous with a narrow strip of supersolidphase separating the two. Approaching transition from the excitonic condensate is announced bysoftening of the excitonic mode at theMpoint of the Brillouin zone. Inside the spin-state orderedphase there is a magnetically ordered state with 2x2 periodicity, which has no precursor in thenormal phase.
